Ultrasound Investigation and the Eye

†University of Miami, Miller School of Medicine, Miami, .
Anesthesiology (Impact Factor: 5.88). 12/2012; 117(6):1396-7. DOI: 10.1097/ALN.0b013e318272d78b
Source: PubMed
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    ABSTRACT: In some cases of severe preeclampsia/eclampsia, brain imaging displays signs compatible with raised intracranial pressure. We aimed to estimate the incidence of raised intracranial pressure in preeclampsia using ocular ultrasonography. Optic nerve sheath diameter (ONSD) measurements were compared in 26 preeclamptic and 25 healthy pregnant women. For each optic nerve, two measurements were made (transverse plane and sagittal plane) using a 7.5 MHz ultrasound linear probe. Preeclamptic patients were followed-up until postpartum day 7. Median ONSD values were significantly greater in preeclamptic patients compared with healthy pregnant women at delivery (5.4 mm (95% CI: 5.2, 5.7) vs. 4.5 mm (95% CI: 4.3, 4.8), P < 0.0001). At delivery, 5/26 (19%) of preeclamptic patients had ONSD values above 5.8 mm (value associated in the literature with 95% risk of raised intracranial pressure) whereas none of the healthy pregnant group had such high ONSD values. In the preeclamptic group, ONSD decreased after the third postpartum day. ONSD values at day 7 were not significantly different from those obtained in the normal pregnancy group (P = 0.10). In about 20% of preeclamptic patients, ONSD reaches values compatible with intracranial pressure above 20 mmHg. Further work is needed to confirm this incidence and to better understand the diagnostic and therapeutic usefulness of this easy-to-do monitoring technique.
    Anesthesiology 01/2012; 116(5):1066-71. DOI:10.1097/ALN.0b013e318246ea1a · 5.88 Impact Factor
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    ABSTRACT: Since Atkinson's original description of retrobulbar block in 1936, needle-based anesthetic techniques have become integral to ophthalmic anesthesia. These techniques are unfortunately associated with rare, grave complications such as globe perforation. Ultrasound has gained widespread acceptance for peripheral nerve blockade, but its translation to ocular anesthesia has been hampered because sonic energy, in the guise of thermal or biomechanical insult, is potentially injurious to vulnerable eye tissue. The US Food and Drug Administration (FDA) has defined guidelines for safe use of ultrasound for ophthalmic examination, but most ultrasound devices used by anesthesiologists are not FDA-approved for ocular application because they generate excessive energy. Regulating agencies state that ultrasound examinations can be safely undertaken as long as tissue temperatures do not increase >1.5°C above physiological levels. Using a rabbit model, we investigated the thermal and mechanical ocular effects after prolonged ultrasonic exposure to single orbital- and nonorbital-rated devices. In a dual-phase study, aimed at detecting ocular injury, the eyes of 8 rabbits were exposed to continuous 10-minute ultrasound examinations from 2 devices: (1) the Sonosite Micromaxx (nonorbital rated) and (2) the Sonomed VuMax (orbital rated) machines. In phase I, temperatures were continuously monitored via thermocouples implanted within specific eye structures (n = 4). In phase II the eyes were subjected to ultrasonic exposure without surgical intervention (n = 4). All eyes underwent light microscopy examinations, followed at different intervals by histology evaluations conducted by an ophthalmic pathologist. Temperature changes were monitored in the eyes of 4 rabbits. The nonorbital-rated transducer produced increases in ocular tissue temperature that surpassed the safe limit (increases >1.5°C) in the lens of 3 rabbits (at 5.0, 5.5, and 1.5 minutes) and cornea of 2 rabbits (both at 1.5 minutes). A secondary analysis of temporal temperature differences between the orbital-rated and nonorbital transducers revealed statistically significant differences (Bonferroni-adjusted P < 0.05) in the cornea at 3.5 minutes, the lens at 2.5 minutes, and the vitreous at 4.0 minutes. Light microscopy and histology failed to elicit ocular injury in either group. The nonorbital-rated ultrasound machine (Sonosite Micromaxx) increases the ocular tissue temperature. A larger study is needed to establish safety. Until then, ophthalmic ultrasound-guided blocks should only be performed with ocular-rated devices.
    Anesthesia and analgesia 04/2012; 115(1):194-201. DOI:10.1213/ANE.0b013e318253622e · 3.47 Impact Factor